The present invention relates to a photographic printing apparatus for printing photographs from negative images. The apparatus has a source of illumination and an optical path directed through a negative frame window for imaging negative frames on photographic printing material. The apparatus further includes a plurality of color filters, displaceable into the optical path, for printing illumination control as well as a video sensor, also displaceable into the optical path, for generating video signals representing high resolution color images of an original negative frame.
In the field of photographic printing technology on various occasions a need has arisen, in addition to producing a photographic print as an optical image of the original negative, to acquire the video content of the negative, point by point and with high resolution, for video reproduction in a different context. A system of this type is known, for example, from German patent No. 42 30 449 which produces so-called xe2x80x9cpackage prints.xe2x80x9d In this system, the original negative frame, illuminated with correct colors, is imaged by means of a tilted mirror into a color television camera, in order to process so-called xe2x80x9cclass photographs.xe2x80x9d Such color television cameras are well known from video technology. They are either equipped as single chip cameras with corresponding pixel-type color filtration for acquisition of the three color separations, or the image is optically divided and passed, through interposition of corresponding color filters, into three different sensor chips, whose images then can be superimposed back together. The latter type of processing is naturally very expensive. Also, the former type of processing is very expensive for high resolution levels (i.e., high pixel numbers) and the color filters are attuned to visual sensitization (i.e., to the sensitivity of the eye). However, this sensitivity deviates considerably from the spectral sensitivity of the normal photographic printing materials. Thus, when these video signals are not only to be reproduced on a screen for viewing, for example, but also to be illuminated on photographic printing material, very expensive color corrections are necessary. These normal color video cameras are used for image acquisition in photographic devices only because, based on their widespread use for video purposes, they are obtainable at relatively reasonable prices, and a rapid acquisition of color originals is possible through the simultaneous generation of the three color images.
In recent times, video signal acquisition has been desired primarily for production of so-called xe2x80x9cindex prints;xe2x80x9d that is, for the greatly reduced reproduction of all pictures of a film on a single sheet, to reproduce for photographers all pictures from their film together with the negative number in the film. Index prints are extremely useful for such things as making subsequent reorders.
When index prints are also to be produced from films that are processed at so-called xe2x80x9cmini-labsxe2x80x9d, the color video cameras customary with high performance devices are still too expensive. On the other hand, speed of image acquisition does not play such an important role.
The principal object of the invention is to provide apparatus of the type described above for video image acquisition that can be justified in terms of its production costs for mini-labs as well.
This object, as well as other objects which will become apparent from the discussion that follows, are achieved, in accordance with the present invention, by providing a black and white video image sensor with a sufficiently high resolution for generating the video signals and by providing means for displacing the color filters into the optical path to provide color separation for the video sensor.
The present invention proceeds from the recognition that black and white image sensors, which in fact need no complicated pixel-type color filtration, or three sensors for each color, are available at reasonable cost. The color filters that are present in color photographic printing equipment are better adapted from the outset to the spectral sensitivity of the printing material than are color filters tuned to visual sensitization in single tube video cameras.
According to one embodiment of the invention, this technique is also applicable to the photographic printing procedure using white light and subtractive post-exposure that is particularly appropriate for simpler color printing devices. Here, so-called xe2x80x9csubtractive filtersxe2x80x9d in the colors of cyan, magenta and yellow are brought into the printing light optical path as so-called xe2x80x9ccolor shuttersxe2x80x9d, if the required amount of printing light in the printing exposure, starting with white light, is incident on the photographic printing material in the colors red, green or blue.
However, since color separation in the basic colors of red, green and blue is required for video signal generation, in each case two of the three filters are simultaneously brought into the illuminating optical path of the original negative to produce, successively, the basic colors of red, green and blue.
According to a particularly preferred embodiment of the invention, an unfiltered planar CCD is provided as a video image sensor.
For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention as illustrated in the accompanying drawings.